OpenAI co-founder John Schulman has left the artificial intelligence startup he co-founded in 2015 for competitor AI firm Anthropic, leaving just three original co-founders still serving the firm.

In addition to Schulman’s departure, OpenAI’s product manager Peter Deng also quietly left the company some time ago while president Greg Brockman is taking an extended leave of absence, according to an Aug. 5 report from The Information.

In an Aug. 6 post to X, Schulman announced his departure from OpenAI after working there for nearly nine years, saying he’d made the “difficult decision” to move to Anthropic to focus on “AI alignment” and pursue more “hands-on technical” work.

OpenAI co-founder leaves for AI rival Anthropic image 0 Source: John Schulman

“I’ve decided to pursue this goal at Anthropic, where I believe I can gain new perspectives and do research alongside people deeply engaged with the topics I’m most interested in,” Schulman wrote on X.

Despite the whirling controversy around OpenAI’s approach to AI safety, research, and regulation , Schulman clarified that he wasn’t leaving the company due to a lack of personal or professional support.

“I'm not leaving due to lack of support for alignment research at OpenAI. On the contrary, company leaders have been very committed to investing in this area,” Schulman said.

“My decision is a personal one, based on how I want to focus my efforts in the next phase of my career.”

Anthropic — a fierce rival of OpenAI — was founded in 2021 by OpenAI’s former vice president of research Dario Amodei and his sister Daniela Amodei, who was also an early employee at the firm.

Related: Microsoft declares OpenAI both ‘strategic partner’ and ‘competition’ in SEC filing

Following the departure of Schulman, only three of the firm’s 11 original founders remain at the company. They include OpenAI CEO Sam Altman, president Greg Brockman, and the firm’s language head Wojciech Zaremba.

Schulman played a key role in the creation of the firm’s AI-powered chatbot ChatGPT, leading OpenAI’s reinforcement training organization, which is responsible for training generative AI models to follow human instructions.

Schulman’s departure comes less than a day after Tesla CEO Elon Musk filed a new lawsuit against OpenAI and Altman.

In the latest filing, Musk alleges Altman “intentionally courted and deceived Musk, preying on Musk’s humanitarian concern about the existential dangers posed by artificial intelligence” and “assiduously manipulated Musk into co-founding their spurious non-profit venture, OpenAI.”

Musk co-founded OpenAI alongside Altman in 2015 and first sued the AI startup in February for allegedly violating promises to operate as a nonprofit.

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